A baby's bottle normally has a closure system which consists of a screw-on cap having a teat or nozzle. A baby sucking on the teat is able to withdraw milk or other liquid inside the bottle. A baby drinking from a bottle as described above frequently encounters the problem of colic which occurs when milk or other liquid and air is ingested by the baby at the same time.
The problem with some existing babies bottles is that the bottle cap with the teat cannot prevent air passing in through the hole in the teat to the interior of the bottle. Such a flow of air occurs automatically due to the partial vacuum which is created in the nozzle when the baby sucks milk through the hole in the teat thus creating the risk of colic. Known closure assemblies also often leak liquid from the bottle.